The present invention relates to the art of earth boring and, more particularly, to a raise boring head for boring raise holes in a mine by enlarging a pilot hole into a raise hole having a larger diameter than the pilot hole.
A relatively large diameter hole may be provided between a first location and a second location in a mine or other underground works by an operation commonly referred to as raise drilling. A raise drilling operation begins by drilling a small diameter pilot hole through the earth from a first location to an opening at the second location using a small diameter pilot bit. After the pilot hole is completed, the pilot bit is removed from the drill string and a large diameter raise bit or raise head attached. The raise head is rotated and drawn along the pilot hole, thereby enlarging the pilot hole to the desired size.
As shown in U.S. Pat. No. 3,659,659 to Carl L. Lichte, patented May 2, 1972, raise bits of the prior art generally include a bit body positioned about a central bit axis with rolling cutters mounted at various distances from the central bit axis for disintegrating the earth formations. The rolling cutters may be locked in place on the bit by various locking mechanisms. For example, locking mechanisms are shown in U.S. Pat. No. 3,203,492 to C. L. Lichte, patented Aug. 31, 1965; in U.S. Pat. No. 3,705,635 to William M. Conn, patented Dec. 12, 1972; and in U.S. Pat. No. 3,612,196 to Robert L. Dixon, patented Oct. 12, 1971. The cutters may be positioned to cut the working face according to various geometries. For example, cutter locations are shown in U.S. Pat. No. RE27,597 to M. L. Talbert, patented Mar. 13, 1973, in U.S. Pat. No. 3,805,901 to William D. Coski, patented Apr. 23, 1974, and in U.S. Pat. No. 3,638,740 to Dan B. Justman, patented Feb. 1, 1972. A lubrication system may be provided to transmit lubricant to the bearings of the rolling cutters, as shown in U.S. Pat. No. 3,675,729 to William J. Neilson, patented July 11, 1972.
In certain large diameter hole boring operations, it is necessary to line the finished borehole with some type of lining material. For example, the hole may be lined to prevent sluffing or erosion of the finished shaft. There may be times, depending on the types of formations being bored, when it is unnecessary to line the entire shaft. In some circumstances it may be desirable to use several different lining thicknesses. In these instances it is generally necessary to provide a finished shaft of a fixed insided diameter. It will therefore be appreciated that a need exists for a raise boring system for boring raise holes of different diameters.